1. Field of the Invention
The present invention relates to an imaging pixel device and a method for generating a signal representing an image of an object. More particularly, the present invention relates to an imaging active pixel device having a nondestructive readout structure.
2. Description of Related Art
Imaging arrays are frequently used to produce an image representing an object. The imaging arrays are typically formed from rows and columns of photodetectors which generate photo-charges proportional to light reflected from the object to be imaged. The photo-charges from each pixel are converted to a signal (charge signal) or a potential representative of the level of energy reflected from a respective portion of the object and the signal or potential is read and processed by video processing circuitry to create the image.
The output nodes of pixels in the same column are usually commonly connected and each pixel in the column is individually controlled to read-out at the common output node. Although the common output node design affords ease of construction and control, it frequently suffers from noise and sensitivity problems, due largely from the capacitive effects of the common connection.
One technique used to improve the quality of the charge signal and thus the image is known as the Adaptive Integration Time ("AIT") technique, in which the read-out charge signal is compared to a predetermined quality criterion, and upon failure of such criterion, the process of charge generation and read-out is repeated to improve the charge signal until the criterion is met. With this technique, there may be repeated read-outs from the same pixel.
The AIT technique produces an improved image but more time is required to produce the image. Particularly, in pixels in which the photo-charges are diffused or lost during read-out, the charge generation and read-out time is further increased and the circuitry required for implementing the AIT technique is much more complex.
Therefore, there is a need for an imaging array which is made up of imaging active pixels which are capable of retaining the photo-charges after read-out and provide improved noise and sensitivity signal characteristics.
The imaging active pixel device and method according to the present invention accomplishes the above needs.